In recent times, an antenna that is incorporated into a foldable cellular phone is mainly disposed like a case where the antenna is disposed on a lower end of a lower casing and a case where the antenna is disposed in an upper casing. However, in all of the cases, it has been known that antenna performance is much affected by a ground structure near the antenna and an adjacent metal conductor.
Further, as a size of a cellular phone is decreased, a length of a casing is decreased, and thus an antenna bandwidth is reduced. According to this trend, a structure has been suggested in which a ground wiring line is disposed near a feeding point of the antenna. However, even in this case, it has been known that a positional relationship between the ground wiring line and a proximity object affects the performance of the antenna.
As an internal antenna for a foldable portable radio apparatus according to the related art, for example, as disclosed in Patent Document 1, a structure has been suggested in which an internal antenna is disposed at a location most spaced apart from a flexible antenna attached to the outside of the casing, and a diversity gain as an antenna system is improved.
Further, as an internal antenna for another foldable portable radio apparatus, as disclosed in Patent Document 2, a plurality of non-feeding elements are disposed near the internal antenna so as to achieve a width bandwidth in the antenna.
Patent Document 1: JP-A-2002-171112
Patent Document 2: JP-A-2003-101335